Where other assemblies that reference your assembly will look. If this number changes, other assemblies have to update their references to your assembly.

AssemblyFileVersion

Used for deployment. You can increase this number for every deployment. It is used by setup programs. Use it to mark assemblies that have the same AssemblyVersion, but are generated from different builds.

In Windows, it can be viewed in the file properties.

If possible, let it be generated by MSBuild. The AssemblyFileVersion is optional. If not given, the AssemblyVersion is used.

I use the format: major.minor.revision.build, where I use revision for development stage (Alpha, Beta, RC and RTM), service packs and hot fixes.

AssemblyInformationalVersion

The Product version of the assembly. This is the version you would use when talking to customers or for display on your website. This version can be a string, like '1.0 Release Candidate'.

Many thanks. We where test crawling our website and noticed a difference in the URLs. Now we know why :) It's already hard to keep consistency when developing applications in a team. Now even need to be more careful with selecting which UrlEncode to use by default.